Modern weapons for tactical warfare include a variety of rapid firing guns adapted for relatively large calibre ammunition. During sustained bursts of gunfire, the mounts for such weapons characteristically are required to withstand repeated shock loads which will vary depending upon factors such as the mass of recoiling parts in the gun and the size of charge in each round. This type of load is typically a high peak stress similar to a sudden hammer blow, and stress fatigue in metals is particularly severe where this type loading is applied. The useful service life of a metal part may be as much as four times longer under continuous loading conditions than for the same part subjected to repeated shock loads.
The foregoing considerations have limited some type of weapons to ground use although they could be most effective in light weight aircraft such as helicopters. Cannons which employ the familiar Gatling principle of operation are an example. Thus, Gatling type weapons produce severe peak loads of the oscillatory type, and cannot be mounted or safely fired in helicopters because of the high risk of metal fatigue resulting in the gun support aircraft structure, as well as control in stability of the vehicle and the weapon both. If gun mounts of sufficient mass and bulk are used on such guns, the resulting installation is too heavy for all but large aircraft, and the weapon becomes totally impractical.